Inheritance 2 Flashcards
(61 cards)
What is transcription?
transcription is where DNA is transcribed and an mRNA molecule is produced
What is translation?
translation is where mRNA (messenger RNA) is translated and an amino acid sequence (protein) is produced
What two stages is the process of turning a gene into a specific sequence of amino acids that in turn make up a specific protein split into?
transcription and translation
Where does transcription occur and what is its role?
in the nucleus of the cell and its role is to produce a copy of a section of DNA in the form of a strand of mRNA
What is the sequence of events for transcription?
-part of the DNA molecule unwinds when hydrogen bonds between the complementary base pairs (A-T, G-C) break
-this exposes the template strand of the gene that codes for the protein being synthesised
-free mRNA nucleotides that are present in the nucleus bind to complementary nucleotides on the template strand
-the mRNA nucleotides are joined to neighbouring nucleotides, forming a single strand of mRNA
-the mRNA molecule leaves the nucleus via a pore in the nuclear envelope
Is the new strand of mRNA formed in transcription a complementary copy of the DNA code from the original gene?
yes
Where does translation occur and what does it result in?
translation occurs in the cytoplasm of the cell and it results in the production of a chain of amino acids that will go on to form a protein
What is the sequence of events for translation?
-after leaving the nucleus, the mRNA molecule attaches to a ribosome and the ribosome moves along the mRNA strand
-in the cytoplasm there are free molecules of tRNA (transfer RNA) ; these tRNA molecules have a triplet of unpaired bases at one end known as the anticodon, and an amino acid at the other
-each specific anticodon corresponds to a specific amino acid
-the anticodon on each tRNA molecule pairs with a complementary triplet (codon) on the mRNA molecule, bringing its specific amino acid along with it
-a second tRNA molecule attaches to its complementary codon (on the mRNA), and a peptide bond is formed between the two neighbouring amino acids
-this process continues until a ‘stop’ codon on the mRNA molecule is reached; this acts as a signal for translation to stop and at this point the amino acid chain coded for by the mRNA molecule is complete
Once the ‘stop’ codon is reached in translation, what happens to the amino acid chain?
this amino acid chain is then folded and modified to form the final protein molecule e.g. an enzyme or antibody
What are mutations?
mutations are rare, random changes that occur in the sequence of DNA bases in a gene or chromosome
Can mutations be inherited?
yes
Do mutations occur continuously?
yes
What can mutations in a gene lead to?
as DNA base sequence determines the sequence of amino acids that make up a protein, mutations in a gene can sometimes lead to a change in the protein that the gene codes for
What do most mutations result in?
most mutations do not alter the protein or only alter it slightly so that its appearance or function is not changed
What is the effect of beneficial mutations?
beneficial mutations change DNA sequence to create new variations of trait that makes organism better adapted to environment, increasing chances of survival
What is the effect of detrimental mutations?
detrimental mutations change DNA sequence to truncate DNA sequence to abrogate normal function of trait
What is the effect of neutral mutations?
neutral mutations have no effect on the functioning of specific characteristics
How can a change in DNA affect the phenotype of an individual?
a change in DNA can affect the phenotype of an individual by altering the sequence of amino acids in a protein
What are the three main ways that the sequence of DNA can be changed (which will alter the sequence of amino acids in the protein)?
INSERTION of a new base into the DNA sequence
DELETION of a base within the DNA sequence
SUBSTITUTION of a base within the DNA sequence
How does the INSERTION method of changing the sequence of DNA work?
a new base is randomly inserted into the DNA sequence
an insertion mutation changed the amino acid that would have been coded for by the group of three bases in which the mutation occurs (every group of three bases (codon) in a DNA sequence codes for an amino acid)
an insertion mutation also has a knock-on effect by changing the groups of three bases further on in the DNA sequence
How does the DELETION method of changing the sequence of DNA work?
a base is randomly deleted from the DNA sequence
like an insertion mutation, a deletion mutation changed the amino acid that would have been coded for by the group of three bases in which the mutation occurs
like an insertion mutation, a deletion mutation also has a knock-on effect by changing the groups of three bases further on in the DNA sequence
How does the SUBSTITUION method of changing the sequence of DNA works?
a base in the DNA sequence is randomly swapped for a different base
unlike an insertion or deletion mutation, a substitution method will only change the amino acid for the group of three bases in which the mutation occurs ; it will not have a knock-on effect
How can a mutation affect the ability of the protein to perform its function?
if the shape of the active site on an enzyme changes, the substrate may no longer be able to bind to the active site
a structural protein (like collagen) may lose its strength if its shape changes
Why do most mutations have a small effect on the protein or organism?
most mutations do not alter the protein or only alter it slightly so that its appearance or function is not changed
therefore there is no effect on the phenotype
